Illuminator and projector

ABSTRACT

An illuminator includes a light source that emits first light that belongs to a first wavelength band, a wavelength converter that converts the first light into second light that belongs to a second wavelength band different from the first wavelength band, and an optical element that transmits the second light emitted from the wavelength converter. An air layer is provided between the wavelength converter and the optical element. A length of the air layer along the direction of the optical axis of the optical element is greater than or equal to 0.3 μm but smaller than or equal to 9.0 μm. The optical element has a coefficient of linear expansion smaller than or equal to 65×10 −7 /° C. at temperatures ranging from 100° C. to 200° C., and a thermal conductivity greater than or equal to 1.0 W/m·K.

The present application is based on, and claims priority from JPApplication Serial Number 2022-023579, filed Feb. 18, 2022, thedisclosure of which is hereby incorporated by reference herein in itsentirety.

BACKGROUND 1. Technical Field

The present disclosure relates to an illuminator and a projector.

2. Related Art

As an illuminator used in a projector, there has been a proposedilluminator using fluorescence emitted from a phosphor when the phosphoris irradiated with excitation light outputted from a light emitter.

JP-A-2017-215549 discloses an illuminator including a light source thatoutputs excitation light, a wavelength converter that converts theexcitation light into fluorescence, and a pickup lens that transmits thefluorescence from the wavelength converter to a downstream opticalsystem. Alight scattering layer having a plurality of recesses isprovided at the surface, of the wavelength converter, that faces thepickup lens.

In the illuminator disclosed in JP-A-2017-215549, the fluorescenceemitted from the wavelength converter is scattered by the lightscattering layer and then enters the pickup lens. Out of thefluorescence that exits out of the light scattering layer, however, aportion of the fluorescence incident on the light incident surface ofthe pickup lens at a large angle of incidence is reflected off the lightincident surface and cannot enter the pickup lens. As a result, theportion of the fluorescence emitted from the wavelength converter islost, resulting in a possible decrease in the fluorescence utilizationefficiency.

SUMMARY

To solve the problem described above, an illuminator according to anaspect of the present disclosure includes a light source that emitsfirst light that belongs to a first wavelength band, a wavelengthconverter that converts the first light into second light that belongsto a second wavelength band different from the first wavelength band,and an optical element that transmits the second light emitted from thewavelength converter. An air layer is provided between the wavelengthconverter and the optical element. A length of the air layer along adirection of an optical axis of the optical element is greater than orequal to 0.3 μm but smaller than or equal to 9.0 μm. The optical elementhas a coefficient of linear expansion smaller than or equal to 65×10⁻⁷/°C. at temperatures ranging from 100° C. to 200° C., and a thermalconductivity greater than or equal to 1.0 W/m·K.

A projector according to another aspect of the present disclosureincludes the illuminator described above, a light modulator thatmodulates light emitted from the illuminator and containing the secondlight, and a projection optical apparatus that projects the lightmodulated by the light modulator.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configuration diagram of a projector according toa first embodiment.

FIG. 2 is a schematic configuration diagram of an illuminator accordingto the first embodiment.

FIG. 3 is a cross-sectional view of a wavelength conversion apparatus inthe first embodiment.

FIG. 4 shows graphs illustrating the relationship of the distancebetween a wavelength converter and an optical element with thetransmittance of a light incident surface of the optical element in thecase where the angle of incidence is 45°.

FIG. 5 shows graphs illustrating the relationship of the distancebetween the wavelength converter and the optical element with thetransmittance of the light incident surface of the optical element inthe case where the angle of incidence is 35°.

FIG. 6 is a schematic configuration diagram of the wavelength conversionapparatus according to Comparative Example 1.

FIG. 7 is a schematic configuration diagram of the wavelength conversionapparatus according to Comparative Example 2.

FIG. 8 is a cross-sectional view of the wavelength conversion apparatusin a second embodiment.

DESCRIPTION OF EXEMPLARY EMBODIMENTS First Embodiment

A first embodiment of the present disclosure will be described belowwith reference to FIGS. 1 to 5 .

In the following drawings, components may be drawn at differentdimensional scales for clarification of each of the components.

An example of a projector according to the present embodiment will bedescribed.

FIG. 1 is a schematic configuration diagram of the projector accordingto the present embodiment.

A projector 1 according to the present embodiment is a projection-typeimage display apparatus that displays color video images on a screenSCR, as shown in FIG. 1 . The projector 1 includes an illuminator 2, acolor separation system 3, light modulators 4R, 4G, and 4B, a lightcombining system 5, and a projection optical apparatus 6. Theconfiguration of the illuminator 2 will be described later.

The color separation system 3 includes a first dichroic mirror 7 a, asecond dichroic mirror 7 b, reflection mirrors 8 a, 8 b, and 8 c, andrelay lenses 9 a and 9 b. The color separation system 3 separatesillumination light WL outputted from the illuminator 2 into red lightLR, green light LG, and blue light LB, guides the red light LR to thelight modulator 4R, guides the green light LG to the light modulator 4G,and guides the blue light LB to the light modulator 4B.

A field lens 10R is disposed between the color separation system 3 andthe light modulator 4R, substantially parallelizes the red light LR, andcauses the resultant light to exit toward the light modulator 4R. Afield lens 10G is disposed between the color separation system 3 and thelight modulator 4G, substantially parallelizes the green light LG, andcauses the resultant light to exit toward the light modulator 4G. Afield lens 10B is disposed between the color separation system 3 and thelight modulator 4B, substantially parallelizes the blue light LB, andcauses the resultant light to exit toward the light modulator 4B.

The first dichroic mirror 7 a transmits the red light LR and reflectsthe green light LG and the blue light LB. The second dichroic mirror 7 breflects the green light LG and transmits the blue light LB. Thereflection mirror 8 a reflects the red light LR. The reflection mirrors8 b and 8 c each reflect the blue light LB.

The red light LR having passed through the first dichroic mirror 7 a isreflected off the reflection mirror 8 a, passes through the field lens10R, and is incident on an image formation region of the light modulator4R for red light. The green light LG reflected off the first dichroicmirror 7 a is further reflected off the second dichroic mirror 7 b,passes through the field lens 10G, and is incident on the imageformation region of the light modulator 4G for green light. The bluelight LB having passed through the second dichroic mirror 7 b travelsvia the relay lens 9 a, the reflection mirror 8 b, the relay lens 9 b,the reflection mirror 8 c, and the field lens 10B and is incident on theimage formation region of the light modulator 4B for blue light.

The light modulators 4R, 4G, and 4B each modulate the color lightincident thereon in accordance with image information to form imagelight. The light modulators 4R, 4G, and 4B are each formed of a liquidcrystal light valve. Although not shown, a light-incident-side polarizeris disposed on the light incident side of each of the light modulators4R, 4G, and 4B. A light-exiting-side polarizer is disposed on the lightexiting side of each of the light modulators 4R, 4G, and 4B.

The light combining system 5 combines the image light outputted from thelight modulator 4R, the image light outputted from the light modulator4G, and the image light outputted from the light modulator 4B with oneanother to form full-color image light. The light combining system 5 isformed of a cross dichroic prism formed of four right-angled prismsbonded to each other. Dielectric multilayer films are formed along thesubstantially X-letter-shaped interfaces between the right-angled prismsbonded to each other.

The image light having exited out of the light combining system 5 isenlarged and projected by the projection optical apparatus 6 to form animage on the screen SCR. That is, the projection optical apparatus 6projects the light modulated by the light modulators 4R, 4G, and 4B. Theprojection optical apparatus 6 is formed of a plurality of projectionlenses.

An example of the illuminator 2 according to the present embodiment willbe described.

In the following description, an XYZ orthogonal coordinate system isused in FIG. 2 . An axis parallel to the chief ray of blue light BLoutputted from a light source apparatus 20 is defined as an axis X. Anaxis parallel to the chief ray of fluorescence YL emitted from awavelength converter 23 is defined as an axis Y. The axis perpendicularto the axes X and Y is defined as an axis Z.

An axis along the chief ray of the blue light BL outputted from thelight source apparatus 20 is referred to as an optical axis ax1 of thelight source apparatus 20. That is, the optical axis ax1 of the lightsource apparatus 20 is parallel to the axis X. The axis along the chiefray of the fluorescence YL emitted from the wavelength converter 23 isreferred to as an optical axis ax2 of the wavelength converter 23. Thatis, the optical axis ax2 of the wavelength converter 23 is parallel tothe axis Y.

FIG. 2 is a plan view showing a schematic configuration of theilluminator 2 viewed in the axis-Z direction.

The illuminator 2 according to the present embodiment includes the lightsource apparatus 20, an afocal system 35, a light separator 21, awavelength conversion apparatus 22, an optical integration system 24, apolarization converter 25, and a superimposing lens 26, as shown in FIG.2 . In FIG. 2 , only the wavelength converter 23 and an optical element28 are shown as the wavelength conversion apparatus 22, and the othercomponents are omitted. The configuration of the wavelength conversionapparatus 22 will be described later in detail.

The light source apparatus 20 includes a plurality of light sources 201.In the present embodiment, the light source apparatus 20 includes fourlight sources 201. The four light sources 201 are arranged separatelyfrom each other in two rows and two columns along the axes Y and Z. Thelight source apparatus 20 outputs the blue light BL, which belongs to afirst wavelength band. The number of light sources 201, which form thelight source apparatus 20, is not limited to a specific number, and thearrangement of the light sources 201 is not limited to a specificarrangement.

The light sources 201 are each formed of a blue semiconductor laser andoutputs blue light BL1, which belongs to the first wavelength band. Theblue semiconductor laser outputs the blue light BL1, which belongs tothe first wavelength band having a peak wavelength that falls within arange, for example, from 380 to 495 nm. The light source apparatus 20therefore outputs four beams of the blue light BL1 as a whole. In thepresent specification, the four beams of the blue light BL1 arecollectively referred to as the blue light BL, and the center axis ofthe entire four beams of the blue light BL1 is referred to as the chiefray of the blue light BL. As will be described later, part of the bluelight BL functions as excitation light that excites a phosphor containedin the wavelength converter 23. The blue light BL1 in the presentembodiment corresponds to the first light in the claims.

In the present embodiment, the light sources 201 each have aconfiguration in which one semiconductor laser chip is accommodated in apackage, what is called a CAN-package-type laser device. The lightexiting surface of a package 202 is provided with a collimator lens 203,which is formed of a convex lens, and the blue light BL1 parallelized bythe collimator lens 203 is outputted. The light sources 201 may insteadeach be a light emitter having a configuration in which a plurality ofsemiconductor laser chips are accommodated in a single package.

The afocal system 35 is provided between the light source apparatus 20and the light separator 21. The afocal system 35 reduces the luminousflux diameter of the blue light BL outputted from the light sourceapparatus 20. The afocal system 35 is formed of a convex lens 351 havingpositive power and a concave lens 352 having negative power. In thepresent embodiment, the afocal system 35 is formed of one convex lensand one concave lens, but the number of lenses that form the afocalsystem 35 is not limited to a specific number.

The light separator 21 is so disposed as to incline by 45° with respectto the optical axes ax1 and ax2. That is, the light separator 21 isprovided in the position where the optical axis ax1 of the light sourceapparatus 20 and the optical axis ax2 of the wavelength converter 23intersect with each other. The light separator 21 is characterized so asto reflect light that belongs to a blue wavelength band and transmitlight that belongs to a yellow wavelength band. The light separator 21therefore reflects the blue light BL outputted from the light sourceapparatus 20 and transmits the fluorescence YL emitted from thewavelength converter 23.

The light separator 21 includes a light transmissive substrate 211 and adichroic mirror 212. The dichroic mirror 212 is provided at the lighttransmissive substrate 211, reflects the blue light BL outputted fromthe light source apparatus 20, and transmits the fluorescence YL emittedfrom the wavelength converter 23. The dichroic mirror 212 is provided atpart of the region of the light transmissive substrate 211 in thepresent embodiment, but the size of the light transmissive substrate 211may instead be reduced to the size of the dichroic mirror 212, and thedichroic mirror 212 may be provided across the entire region of thelight transmissive substrate 211.

FIG. 3 is a cross-sectional view of the wavelength conversion apparatus22.

The wavelength conversion apparatus 22 includes the wavelength converter23, the optical element 28, a first heat dissipating member 29, areflection mirror 30, a second heat dissipating member 32, and a spacer33, as shown in FIG. 3 .

The wavelength converter 23 converts the blue light BL having exited outof the optical element 28 into the fluorescence YL, which belongs to asecond wavelength band different from the first wavelength band. Thewavelength converter 23 contains a ceramic phosphor that converts theblue light BL into the yellow fluorescence YL. The second wavelengthband ranges, for example, from 490 to 750 nm, and the fluorescence YL isyellow light containing the green light component and the red lightcomponent. The phosphor may contain a monocrystalline phosphor. Thewavelength converter 23 has a substantially square planar shape whenviewed in the direction in which the blue light BL is incident (axis-Ydirection). The wavelength converter 23 has a first surface 23 a, whichfaces the optical element 28, and a second surface 23 b opposite fromthe first surface 23 a. The fluorescence YL in the present embodimentcorresponds to the second light in the claims.

Specifically, the wavelength converter 23 contains, for example, anyttrium-aluminum-garnet-based (YAG-based) phosphor. Consider YAG:Ce,which contains cerium (Ce) as an activator, by way of example, and theYAG:Ce phosphor can be made, for example, of a material produced bymixing raw powder materials containing Y₂O₃, Al₂O₃, CeO₃, and otherconstituent elements with one another and causes the mixture to undergoa solid-phase reaction, Y—Al—O amorphous particles produced by using acoprecipitation method, a sol-gel method, or any other wet method, orYAG particles produced by using a spray-drying method, a flame-basedthermal decomposition method, a thermal plasma method, or any othergas-phase method. The cerium (Ce) content ranges from about 0.1 to 1 mol% vol. The wavelength converter 23 having the cerium content describedabove can efficiently generate yellow fluorescence.

The wavelength converter 23 contains a scattering element that scattersthe blue light BL and the fluorescence YL. The scattering element is aplurality of pores 39 formed in the phosphor. It is effective that thesize of the pores 39 is equal to or smaller than the wavelength of thefluorescence YL, because the fluorescence YL is not absorbed when thefluorescence YL is reflected at the interface between the pores 39 andthe fluorophore. In particular, the size of the pores 39 may be greaterthan or equal to 1/10 the wavelength of the fluorescence YL but smallerthan or equal thereto, desirably about ¼ the wavelength. The scatteringcaused by the scattering element is Mie scattering. The plurality ofpores 39 can be created, for example, by lowering the sinteringtemperature used when the material of wavelength converter 23 issintered and stopping the sintering process halfway through, or bymixing a pore forming resin with the material of wavelength converter 23and sintering the mixture. The fluorescence YL generated in the phosphoris scattered by the pores 39 and emitted out of the wavelength converter23. Out of the blue light BL having entered the wavelength converter 23,part of the blue light BL is converted in terms of wavelength into thefluorescence YL, whereas the other part of the blue light BL isbackscattered by the pores 39 and caused to exit out of the wavelengthconverter 23 without undergoing the wavelength conversion.

The optical element 28 is provided between the light separator 21 andthe wavelength converter 23. The optical element 28 includes a planarplate part 37 and a lens part 38. The lens part 38 is formed at onesurface of the planar plate part 37 integrally therewith. The opticalelement 28 is so configured that the lens part 38 faces the lightseparator 21 and the planar plate part 37 faces the wavelength converter23. The planar plate part 37 has a third surface 37 a, via which theblue light BL exits and on which the fluorescence YL and the blue lightBL are incident. The lens part 38 has a hemispherical surface 38 a, onwhich the blue light BL is incident and via which the fluorescence YLand the blue light BL exit, and has positive power. The center of thehemispherical surface 38 a is located on the first surface 23 a of thewavelength converter 23. The lens part 38 focuses the blue light BL thatexits out of the light separator 21 and causes the focused blue light BLto enter the wavelength converter 23. Furthermore, the lens part 38converts the angular distribution of the fluorescence YL and the bluelight BL that exit out of the wavelength converter 23 and causes theresultant light to exit. The center axis of the hemisphere that formsthe shape of the lens part 38 is defined as an optical axis ax3 of theoptical element 28. The center axis ax3 of the optical element 28coincides with the optical axis ax2 of the wavelength converter 23.

The optical element 28 is made of a light transmissive material having asmall coefficient of linear expansion. The YAG fluorophore in thewavelength converter 23 generates heat, and the maximum temperature atwhich the YAG fluorophore can maintain its light emission efficiency isapproximately 200° C., so that heat is generated at temperatures lowerthan or equal to 200° C. When heat is generated, the temperature of theoptical element 28 in the vicinity of the region, of the wavelengthconverter 23, that is irradiated with the blue light BL rises, so thatthe optical element 28 partially expands. Since the expansion of theoptical element 28 occurs in the vicinity of the light irradiatedregion, there is a risk of damage to the optical element 28 due tointernal stress induced as a result of the difference in the amount ofexpansion between the region in the vicinity of the light irradiatedregion and the region away therefrom. It is therefore desirable that thecoefficient of linear expansion of the optical element 28 is small tosuppress the damage to the optical element 28.

Specifically, the coefficient of linear expansion of the optical element28 is desirably smaller than or equal to 65×10⁻⁷/° C., more desirably,smaller than or equal to 55×10⁻⁷/° C. at temperatures ranging from 100°C. to 200° C. The coefficient of linear expansion of ordinary whitesheet glass is about 93×10⁻⁷/° C., which exceeds 65×10⁻⁷/° C. If theoptical element is made of ordinary white plate glass, the opticalelement breaks in many cases. In contrast, an optical element made, forexample, of H3 glass (manufactured by Okamoto Glass Co., Ltd.), one ofborosilicate glass products, S-LAL 21 (manufactured by OHARA INC.), orquartz glass does not break. The coefficients of linear expansion of theglass materials described above are all smaller than or equal to55×10⁻⁷/° C. at temperatures ranging from 100° C. to 200° C.

Instead, to suppress the heat concentration described above, the opticalelement 28 may be made of a material having a thermal conductivitygreater than or equal to 7 W/m·K, such as magnesium oxide or any otherthermally conductive transparent ceramic material, fluorite, and quartz.Even when the thermal conductivity is about 1 W/m·K, such as the thermalconductivity of Pyrex (registered trademark), however, a heatdistribution effect can be achieved without thermal damage as long asthe coefficient of linear expansion is smaller than or equal to65×10⁻⁷/° C. That is, the optical element 28 only needs to be made of amaterial characterized in that heat distribution prevents thermal stressconcentration. Furthermore, S-LAL21, magnesium oxide, and othersimilarly characterized materials are desirable also in that they havehigh refractive indices and excel in the function as a pickup lens.Calcium fluoride having a refractive index of 1.45 can also be used asthe material of the optical element 28. Calcium fluoride has anadvantage of being soft and readily polished, and further has a highthermal conductivity of 9 W/m·K. It is therefore more desirable that theoptical element 28 is made of a material having both a low coefficientof linear expansion and high thermal conductivity, such as quartz,sapphire, fluorite, and magnesium oxide.

As described above, the optical element 28 receives the heat from thewavelength converter 23 and has the function as a heat sink as well asthe function of a pickup lens. It is therefore desirable that theoptical element 28 has high thermal conductivity, and that the productof the specific heat, the density, and the volume of the optical element28 is greater than or equal to the product of the specific heat, thedensity, and the volume of the wavelength converter 23. The heatcapacity defined by the specific heat×the density×the volume is ayardstick of the performance of a heat sink. The YAG fluorophore thatforms the wavelength converter 23 has a specific heat of 600 J/kg·K, adensity of 4.55, and a thickness of 50 μm. Therefore, in a 1-mm-cubicwavelength converter 23, the heat capacity is 1.36×10⁻⁹ J/K, which is avery small value. The optical element 28 therefore functions adequatelyas a heat sink.

For example, the glass that forms the optical element 28 has a specificheat ranging from 800 to 900 J/kg·K and has a density of about 2.5, sothat the heat capacity of the glass optical element 28 is only 82% ofthat of the YAG fluorophore. Since the optical element 28 can be thickerthan or equal to 1 mm, however, the heat capacity of the optical element28 can be 16 times greater than or equal to the heat capacity of thewavelength converter 23. It is noted that since copper has a specificheat of 900 J/kg·K and a density of 9, the heat capacity of copper is 60times the heat capacity of the wavelength converter 23 provided that thethickness is 1 mm. The heat capacity of glass is about 28% of that ofcopper, and quartz crystal and calcium fluoride crystal havesubstantially the same heat capacity as that of glass, so that thesematerials therefore form effective coolers.

Setting the volume of the optical element 28 to be 1×10⁴ times,desirably, 1×10³ times the volume of the wavelength converter 23 allowsthe heat capacity to increase substantially in proportion to the volume,whereby the heat generated by the wavelength converter 23 can be greatlysuppressed. For example, when the optical element 28 is made of lighttransmissive alumina, and assuming that the volume of the opticalelement 28 is 1×10⁴ times the volume of the wavelength converter 23having the dimensions of 1 mm×1 mm×50 μm, that is, the length of oneside of the optical element 28 is 10 times one side of the wavelengthconverter 23, and the thickness of the optical element 28 is 100 timesthe thickness of the wavelength converter 23, so that the volume of theoptical element 28 is 10 mm×10 mm×5 mm, the heat capacity of the opticalelement 28 is 0.015 J/K. That is, heat equivalent to 1.5 W raises thetemperature of the optical element 28 by 100° C. When the volume of theoptical element 28 is 1×10³ times the volume of the wavelength converter23 having the dimensions of 1 mm×1 mm×50 μm, the heat equivalent to 15 Wraises the temperature of the optical element 28 by 100° C. This levelof heat sink performance of the optical element 28 is sufficient forsurface cooling of the wavelength converter 23. For example, incidenceof the blue light BL equivalent to 50 to 100 W generates heat equivalentto about 40 W. Therefore, 15 W in the optical element 28 is 40% of thetotal generated heat, and the optical element 28 serves as a sufficientauxiliary heat sink. When the heat capacity of the optical element 28 is0.015 J/K, the cooling performance is preferably further increased.

To this end, in the present embodiment, the first heat dissipatingmember 29 is provided at the side surface of the optical element 28. Thefirst heat dissipating member 29 is thermally coupled to the opticalelement 28. That is, the first heat dissipating member 29 may be indirect contact with the optical element 28 or may be coupled therewithvia any heat transfer member. The first heat dissipating member 29 ismade of a material having relatively high density, for example, copper,aluminum, iron, and alumina. The performance of the first heatdissipating member 29 as a heat sink is thus improved, whereby theperformance of cooling the wavelength converter 23 can be furtherincreased. The first heat dissipating member 29 in the presentembodiment corresponds to the heat dissipating member in the claims.

The reflection mirror 30 is provided at a circumferential edge portion,of the hemispherical surface 38 a of the lens part 38, that is far fromthe optical axis ax3. In other words, the reflection mirror 30 has acircular opening 30 h around the optical axis ax3. The reflection mirror30 is formed of a dielectric multilayer film formed at the lens part 38.Specifically, the opening 30 h having an opening angle of 74° is set inthe vicinity of the apex of the hemispherical surface 38 a, and thedielectric multilayer film is formed around the opening 30 h. Even whenthe fluorescence YL or the blue light BL that passes through the opening30 h becomes a slightly divergent beam, a downstream parallelizing lenscan, for example, added to produce a beam with the divergencesuppressed. On the other hand, the fluorescence YL or the blue light BLthat has not passed through the opening 30 h but has been reflected offthe reflection mirror 30 traces back the path and enters the wavelengthconverter 23. When the opening angle of the opening 30 h is 74°, thereflection mirror 30 is designed to reflect the fluorescence YL by theamount equal to half the light intensity thereof to the wavelengthconverter 23.

The second heat dissipating member 32 is provided at the second surface23 b of the wavelength converter 23 via a bonding layer 40. In detail,the second surface 23 b of the wavelength converter 23 is so polishedthat surface roughness Ra is smaller than or equal to 10 nm, areflection coating formed of a dielectric multilayer film is provided atthe second surface 23 b, and a low-refractive-index layer made ofair-containing nano-silica and having a refractive index of smaller thanor equal to 1.3 is provided at the reflection coating. The order inaccordance with which the dielectric multilayer and thelow-refractive-index layer are layered on each other may be reversed.When the low-refractive-index layer is provided at the second surface 23b, the low-refractive-index layer can fill recesses formed on the secondsurface 23 b by the plurality of pores 39, so that the reflectionperformance of the dielectric multilayer film is readily achieved. Thebonding layer 40 is made, for example, of solder. The second heatdissipating member 32 is made of metal, for example, copper. Part of theheat generated by the wavelength converter 23 is dissipated out thereofby the second heat dissipation member 32 via the second surface 23 b. Asdescribed above, the wavelength converter 23 has a reflection layerdisposed at the second surface 23 b of the wavelength converter 23 andformed, for example, of a dielectric multilayer film, and the reflectionlayer reflects the blue light BL and the fluorescence YL toward theoptical element 28.

The spacer 33 is provided between the wavelength converter 23 and theoptical element 28. The spacer 33 maintains the distance between thewavelength converter 23 and the optical element 28. The shape of thespacer 33 is not limited to a specific shape, and the number of spacers33 is not limited to a specific number. The wavelength converter 23 andthe optical element 28 are thus separate from each other, and an airlayer 41 is provided between the wavelength converter 23 and the opticalelement 28. The air layer 41 has a length G1 along the direction of theoptical axis ax3 of the optical element 28 and greater than or equal to0.3 μm but smaller than or equal to 9.0 μm. The rationale for the reasonwhy the length G1 of the air layer 41 along the direction of the opticalaxis ax3 of the optical element 28 is set so as to fall within the rangedescribed above will be described later.

Specifically, the spacer 33 having a height greater than or equal to 0.3μm but smaller than or equal to 9.0 μm is formed at a circumferentialedge portion of the first surface 23 a of the wavelength converter 23.The spacer 33 is formed, for example, by printing silicone resincontaining a gap agent having a diameter greater than or equal to 0.3 μmbut smaller than or equal to 9.0 μm on either the wavelength converter23 or the optical element 28 and by sintering the resultant structure.Instead, glass is printed on the circumferential edge portion of thefirst surface 23 a of the wavelength converter 23 to a thickness greaterthan or equal to 0.3 μm but smaller than or equal to 9.0 μm, bonding thewavelength converter 23 and the optical element 28 to each other, andsintering the resultant structure. An air gap having the thicknessranging from 0.3 μm to 9.0 μm is thus formed between the wavelengthconverter 23 and the optical element 28. In this state, the wavelengthconverter 23 and the optical element 28 are fixed to each other. Forexample, the wavelength converter 23 and the optical element 28 may bebonded to each other with an adhesive made of resin or any othermaterial, or may be mechanically fixed to each other with a spring orany other elastic member.

As will be described later, the distance between wavelength converter 23and the optical element 28, that is, the length G1 of the air layer 41ranges from somewhere around the wavelength to several tens of times thewavelength, and the wavelength converter 23 and the optical element 28are disposed sufficiently close to each other. The fluorescence YLemitted from the wavelength converter 23 is emitted in the form of lighthaving the Lambertian distribution. Since the wavelength converter 23 isin close proximity to the optical element 28, however, the fluorescenceYL incident on the optical element 28 at large angles of incidencetravels back and forth between the optical element 28 and the wavelengthconverter 23, and repeatedly enters the wavelength converter 23 and isscattered therein. The fluorescence YL thus enters the optical element28 during the travel along the short distance.

For example, the distance required for a beam incident on the opticalelement 28 at an angle of incidence of 86° to be reflected 6 times offthe optical element 28 within a distance of 1 μm is 6×tan 86°×1 μm=86μm, which causes the fluorescence YL to diverge by an acceptable amount.That is, the fluorescence YL enters the optical element 28 or thewavelength converter 23 while traveling over the distance of 86 μm. Thewavelength converter 23 contains the pores 39 having the size rangingfrom about 0.1 μm to 1 μm and being present in a volume of 2 μm×2×2 μmat a count of about 1 or 2, so that the fluorescence YL having enteredthe wavelength converter 23 is scattered by the pores 39 and outputtedfrom the wavelength converter 23 and enters the optical element 28. Thefluorescence YL emitted from the wavelength converter 23 is thus hardlylost but enters the optical element 28.

In the present embodiment, since the afocal system 35 is providedbetween the light source apparatus 20 and the light separator 21, theblue light BL is incident on the dichroic mirror 212 with the luminousflux diameter of the blue light BL reduced, as shown in FIG. 2 . Thesize of the dichroic mirror 212 can therefore be reduced as comparedwith a case where no afocal system 35 is provided. In addition, theconcave lens 352 of the afocal system 35 can reduce aberrationsassociated with the blue light BL focused on the wavelength converter23. Since the dichroic mirror 212 is characterized so as to transmit theyellow light component, a central luminous flux of the fluorescence YLemitted from the wavelength converter 23 passes through the opticalelement 28 and then passes through the dichroic mirror 212. Theperipheral luminous flux of the fluorescence YL emitted from thewavelength converter 23 is not incident on the dichroic mirror 212 butpasses through the light transmissive substrate 211 or the space outsidethe light separator 21.

Out of the blue light BL having exited out of the wavelength converter23, a central luminous flux is incident on the dichroic mirror 212, butthe peripheral luminous flux is not incident on the dichroic mirror 212but passes through the light transmissive substrate 211 or the spaceoutside the light separator 21. A central luminous flux of the bluelight BL incident on the dichroic mirror 212 is reflected off thedichroic mirror 212 and lost. On the other hand, the blue light BL thatis not incident on the dichroic mirror 212 is used as illumination lightWL along with the fluorescence YL. In this case, reducing the size ofthe dichroic mirror 212 can reduce the amount of blue light BL reflectedoff the dichroic mirror 212 and lost.

The blue light BL and the fluorescence YL thus enter the opticalintegration system 24. The blue light BL and the yellow fluorescence YLare combined with each other into the illumination light WL, which iswhite light.

The optical integration system 24 includes a first multi-lens array 241and a second multi-lens array 242. The first multi-lens array 241includes a plurality of first lenses 2411, which divide the illuminationlight WL into a plurality of sub-luminous fluxes.

The lens surface of the first multi-lens array 241, that is, thesurfaces of the first lenses 2411 are conjugate with the image formationregion of each of the light modulators 4R, 4G, and 4B. Therefore, whenviewed in the direction of the optical axis ax2, the first lenses 2411each have a rectangular shape substantially similar to the shape of theimage formation region of each of the light modulators 4R, 4G, and 4B.The sub-luminous fluxes having exited out of the first multi-lens array241 are thus each efficiently incident on the image formation region ofeach of the light modulators 4R, 4G, and 4B.

The second multi-lens array 242 includes a plurality of second lenses2421 corresponding to the plurality of first lenses 2411 of the firstmulti-lens array 241. The second multi-lens array 242 along with thesuperimposing lens 26 brings images of the first lenses 2411 of thefirst multi-lens array 241 into focus in the vicinity of the imageformation region of each of the light modulators 4R, 4G, and 4B.

The illumination light WL having passed through the optical integrationsystem 24 enters the polarization converter 25. The polarizationconverter 25 has a configuration in which polarization separation filmsand retardation films that are not shown are arranged in an array. Thepolarization converter 25 aligns the polarization directions of theillumination light WL with a predetermined direction. Specifically, thepolarization converter 25 aligns the polarization directions of theillumination light WL with the direction of the transmission axis of thelight-incident-side polarizers for the light modulators 4R, 4G, and 4B.

The polarization directions of the red light LR, the green light LG, andthe blue light LB separated from the illumination light WL having passedthrough the polarization converter 25 coincide with the transmissionaxis direction of the light-incident-side polarizers for the lightmodulators 4R, 4G, and 4B. The red light LR, the green light LG, and theblue light LB are therefore incident on the image formation regions ofthe light modulators 4R, 4G, and 4B, respectively, without being blockedby the light-incident-side polarizers.

The illumination light WL having passed through the polarizationconverter 25 enters the superimposing lens 26. The superimposing lens26, in cooperation with the optical integration system 24, homogenizesthe illuminance distribution in the image formation region of each ofthe light modulators 4R, 4G, and 4B, which are illumination receivingregions.

Comparable Examples

Wavelength conversion apparatuses according to Comparative Examples willbe descried below.

FIG. 6 is a schematic configuration diagram of a wavelength conversionapparatus 200 according to Comparative Example 1.

The wavelength conversion apparatus 200 according to Comparative Example1 includes a wavelength converter 223 and a pickup lens 224, as shown inFIG. 6 . The wavelength converter 223 and the pickup lens 224 aredisposed via an air layer 225. A distance G2 between the wavelengthconverter 223 and the pickup lens 224 is, for example, 0.5 mm. When thedistance G2 between the wavelength converter 223 and the pickup lens 224is large as described above, heat generated, if any, by the wavelengthconverter 223 does not cause a risk of damage to the pickup lens 224because the heat transferred from the wavelength converter 223 to thepickup lens 224 is small.

The wavelength conversion apparatus 200 according to Comparative Example1, however, has the following problems.

For example, consider a case where the pickup lens 224 has a refractiveindex of 1.4. Out of the fluorescence YL emitted from the wavelengthconverter 223, fluorescence YL1 incident on a light incident surface 224a of the pickup lens 224 at angles of incidence smaller than 45° isrefracted at the light incident surface 224 a, enters the pickup lens224, and exits out of the pickup lens 224 in the form of thefluorescence YL1 having a luminous flux diameter W2. In contrast,fluorescence YL2 incident on the light incident surface 224 a at anglesof incidence greater than or equal to 45° is reflected off the lightincident surface 224 a and cannot enter the pickup lens 224.

When a wavelength converter containing a scattering element such aspores is excited, the fluorescence from the wavelength converter isemitted in the Lambertian scheme according to the cosine law. Therefore,in the wavelength conversion apparatus 200 according to ComparativeExample 1, out of the fluorescence emitted from the wavelength converter223, about 4% of the fluorescence YL2 is reflected off the lightincident surface 224 a of the pickup lens 224, undergoes reflectionbetween the wavelength converter 223 and the pickup lens 224, and leaksout of the wavelength conversion apparatus 200. In detail, most of theS-polarized light incident on the light incident surface 224 a of thepickup lens 224 at angles of incidence greater than or equal to 75°leaks out of the wavelength converter apparatus 200. The losscorresponds to 4% of the fluorescence emitted from wavelength converter223.

Furthermore, when an optical system that causes part of the fluorescencein the pickup lens to return to the wavelength converter via areflection mirror to narrow the luminous flux diameter of the light thatexits out of the pickup lens, what is called a recycling optical systemis employed, the fluorescence YL2 having returned to the wavelengthconverter 223 is scattered by the internal pores, causing Lambertreflection. In this case, the behavior of the fluorescence YL2 followsthe cosine law as the behavior of the emitted fluorescence YL2 does, sothat 4% of the fluorescence YL2 that enters the pickup lens 224 isreflected off the surface of the air gap between the wavelengthconverter 223 and the pickup lens 224 and lost. The phenomenon isrepeated in the recycling optical system, so that the 4% loss describedabove accumulates, resulting in a large amount of loss of thefluorescence. For example, when 50% of the fluorescence is recycled and4% of the recycled fluorescence is lost, the total loss is 4+2+1+0.5+ .. . =8%, which is a large amount of loss. The recycling thus at leastdoubles even a small loss, so that it is difficult to employ a recyclingoptical system.

FIG. 7 is a schematic configuration diagram of a wavelength conversionapparatus 300 according to Comparative Example 2.

The wavelength conversion apparatus 300 according to Comparative Example2 includes a wavelength converter 323 and a pickup lens 324, as shown inFIG. 7 . The wavelength converter 323 and the pickup lens 324 aredisposed so as to be in contact with each other. That is, no air layeris present between the wavelength converter 323 and the pickup lens 324.According to the configuration described above, there is no loss of thefluorescence caused by the gap between the wavelength converter and thepickup lens, unlike in Comparative Example 1.

When the pickup lens 324 is in contact with the wavelength converter323, however, no refraction occurs at a light incident surface 324 a ofthe pickup lens 324, and fluorescence YL3 travels through the interiorof the pickup lens 324 with the Lambertian distribution maintained. As aresult, a luminous flux diameter W3 of the fluorescence YL3 that exitsout of the pickup lens 324 is greater than the luminous flux diameter W2in Comparison Example 1. Therefore, in Comparative Example 2, theetendue of the wavelength conversion apparatus 300 is greater than thatin Comparative Example 1, so that the light utilization efficiency in adownstream optical system decreases.

The present inventor therefore considered that providing the very thinair layer 41 between the optical element 28, which functions as a pickuplens, and the wavelength converter 23 could solve the problems with thewavelength conversion apparatuses according to Comparative Examples 1and 2. The present inventor conducted a simulation for determining theminimum distance between the wavelength converter 23 and the opticalelement 28 (length G1 of air layer 41).

As the simulation, consider a situation in which the fluorescence YLemitted from wavelength converter 23 passes through the air layer 41 andreaches the third surface 37 a of the optical element 28 at a specificangle of incidence, and the amount of the fluorescence YL incident onthe third surface 37 a at the specific angle of incidence, passingtherethrough, and entering the optical element 28 is calculated. Thesimulation was conducted under the following conditions: The refractiveindex of the wavelength converter 23 was 1.8; the refractive index ofthe optical element 28 was 1.8; the refractive index of the air layer 41was 1.0; and the distance between the wavelength converter 23 and theoptical element 28 (length G1 of air layer 41) was varied. Thecalculation was also performed under the condition of using twodifferent angles of incidence, 45° and 35°. The angle of incidence of45° is the angle at which the fluorescence YL is totally reflected offthe third surface 37 a of the optical element 28, and the angle ofincidence of 35° is the critical angle at which the fluorescence YL istotally reflected off the third surface 37 a of the optical element 28.

FIG. 4 shows graphs illustrating the relationship of the distancebetween the wavelength converter 23 and the optical element 28 with thetransmittance of the third surface 37 a of the optical element 28 in thecase where the angle of incidence is 45°. FIG. 5 shows graphsillustrating the relationship of the distance between the wavelengthconverter 23 and the optical element 28 with the transmittance of thethird surface 37 a of the optical element 28 in the case where the angleof incidence is 35°. In FIGS. 4 and 5 , the horizontal axis representsthe distance (μm) between the wavelength converter 23 and the opticalelement 28. The vertical axis represents the transmittance (%). Thetransmittance in FIGS. 4 and 5 is defined as follows: Provided that thetotal amount of fluorescence YL incident on the third surface 37 a ofthe optical element 28 at the angle of incidence of 45° or 35° is 100%,the transmittance is the proportion of the fluorescence having passedthrough the third surface 37 a and entered the optical element 28.

When fluorescence YL enters the air layer 41 from the wavelengthconverter 23, and when the fluorescence YL passes through the air layer41 as an evanescent wave and enters the optical element 28, thetransmittance increases even though the angle of incidence causes totalreflection because no total reflection occurs, as shown in FIGS. 4 and 5. That is, in the region where the distance (length G1 of air layer 41)is sufficiently small, the fluorescence YL does not recognize the airlayer 41, so that the fluorescence YL passes through the interfacebetween the air layer 41 and the optical element 28 without beingrefracted at the interface. In contrast, in the region where thedistance (length G1 of air layer 41) is large, the fluorescence YLrecognizes the air layer 41, so that the fluorescence YL is totallyreflected off the interface between the air layer 41 and the opticalelement 28. That is, in the region where the length G1 of the air layer41 is large, Snell's law of refraction holds. In this case, the luminousflux diameter of the fluorescence YL passing through the interfacebetween the air layer 41 and the optical element 28 can be reduced, asdescribed in the paragraph relating to Comparative Example 1. Therefraction of the fluorescence at the interface between the air layer 41and the optical element 28 allows reduction in the etendue, which isuseful for a focusing optical system of a projector or any other similarapparatus.

The results of the simulation show that when the distance between thewavelength converter 23 and the optical element 28 is very small, thefluorescence YL emitted from the wavelength converter 23 passes throughthe air layer 41 without being refracted as an evanescent wave.Specifically, when the angle of incidence is 45°, the transmittance atwhich the air layer 41 transmits both the P-polarized light andS-polarized light of the fluorescence YL increases in the region wherethe distance between the wavelength converter 23 and the optical element28 is smaller than 0.3 μm, as shown in FIG. 4 . In this case, thefluorescence YL emitted from wavelength converter 23 is not refracted atthe interface between the air layer 41 and the optical element 28 buttravels straight and becomes a more divergent beam after exiting out ofthe optical element 28, so that part of the fluorescence YL cannot entera downstream optical system. In the case of the angle of incidence of45°, when the distance between the wavelength converter 23 and theoptical element 28 is greater than or equal to 0.3 μm, the fluorescenceYL is refracted at the interface between the air layer 41 and theoptical element 28 and enters the optical element 28.

When the angle of incidence is 35°, and when the distance between thewavelength converter 23 and the optical element 28 is greater than orequal to 0.9 μm, the fluorescent YL is refracted at the interfacebetween the air layer 41 and the optical element 28 and enters theoptical element 28 regardless of whether the fluorescent YL isP-polarized or S-polarized although the P polarized light and the Spolarized light slightly differ from each other in terms of behavior, asshown in FIG. 5 . Based on the results described above, when thedistance between the wavelength converter 23 and the optical element 28is greater than or equal to 0.3 μm, desirably, greater than or equal to0.9 μm, the fluorescence YL emitted from the wavelength converter 23 isrefracted at the interface between the air layer 41 and the opticalelement 28 (third surface 37 a of optical element 28) and enters theoptical element 28.

The present inventor then studied the maximum distance between thewavelength converter 23 and the optical element 28 (length G1 of airlayer 41).

A simulation shows that the reflectance at which the wavelengthconverter 23 or the optical element 28 reflects the fluorescence YLexceeds 80% when the angle of incidence is 86°. On the other hand, sincethe fluorescence YL is emitted from the wavelength converter 23 in theLambertian scheme, the proportion of the emitted luminous flux withrespect to the total luminous flux becomes 0.18% when the angle ofemission is 83° provided that the emission follows the cosine law. Theamount of fluorescence YL over the range from the angle of incidence of83° to the angle of incidence of 86° is 0.15%, so that the calculationis performed by assuming that most of the reflected fluorescence YLincident at angles of incidence smaller than or equal to 83° is incidentat angles of incidence greater than or equal to 86°.

Provided that the amount of fluorescent YL incident on the third surface37 a of the optical element 28 over the range from the angle ofincidence of 83° to the angle of incidence of 86° is 100%, the amount offluorescent YL reflected off the third surface 37 a and incident on thefirst surface 23 a of the wavelength converter 23 is smaller than orequal to 80%. On the other hand, the amount of fluorescence YL thatenters the wavelength converter 23 is greater than or equal to 20%. Theamount of fluorescence YL that enters the wavelength converter 23 istherefore 80%×20%=16%. Similarly, the amount of fluorescence YLreflected again off the optical element 28 and then reflected off thefirst surface 23 a of the wavelength converter 23 is smaller than orequal to 80%×80%×80%×80%=41%. The amount of component that remains asspecularly reflected light is smaller than or equal to 0.2%×41%=0.08%.That is, when the fluorescence YL is reflected twice off the firstsurface 23 a of the wavelength converter 23, 59% of the amount offluorescence YL enters the wavelength converter 23. The amount offluorescence YL entering the wavelength converter 23 is a small valuesmaller than or equal to 0.08% of the total amount of emittedfluorescence YL.

The fluorescence YL having entered the wavelength converter 23 isscattered by the pores 39 in the wavelength converter 23 and is emittedagain as Lambertian diffused light from the wavelength converter 23.Most of the fluorescence YL therefore enters the optical element 28.That is, when the specularly reflected light incident at the angle ofincidence of 83° reaches twice the first surface 23 a of the wavelengthconverter 23, 0.08% of the fluorescence YL becomes the specularlyreflected light, and the other fluorescence YL enters the opticalelement 28. The fluorescence YL that is lost as the specularly reflectedlight traveling sideways from the gap between the wavelength converter23 and the optical element 28 is negligible.

Provided that the blue light BL at the first surface 23 a of thewavelength converter 23 has a 1-mm square size, and allowable divergenceof the fluorescence YL is 0.1 mm, the allowable value of 0.1 mm isachieved after four times of specular reflection at the angle ofincidence of 86° with the distance between the wavelength converter 23and the optical element 28 being 2 μm. Provided that the allowabledivergence of the fluorescence YL is 0.25 mm, which is one-fourth thesize of the blue light BL, the allowable value of 0.25 mm is achievedafter four times of specular reflection at the angle of incidence of 86°with the distance between the wavelength converter 23 and the opticalelement 28 being 4 μm. Provided that the allowable divergence of thefluorescence YL is 0.5 mm, which is half the size of the blue light BL,the allowable value of 0.5 mm is achieved after four times of specularreflection at the angle of incidence of 86° with the distance betweenthe wavelength converter 23 and the optical element 28 being 9 μm. Asdescribed above, it is desirable that the distance between thewavelength converter 23 and the optical element 28 is smaller than orequal to 9 μm, more desirably, smaller than or equal to 4 μm, and stillmore desirably, smaller than or equal to 2 μm.

The distance between the wavelength converter 23 and the optical element28 will next be examined from the viewpoint of thermal conductivity.

Since the thermal conductivity of air is about 0.03 W/m·K, in order forthe heat capacity of the air layer 41 to be comparable to that of thewavelength converter 23 having a thickness of 50 μm, the thickness ofthe air layer 41 is 0.03/(7/50 μm)=0.2 μm, provided that the thermalconductivity of the YAG phosphor that constitutes the wavelengthconverter 23 is 7 W/m·K. Therefore, from a thermal point of view, thedistance between the wavelength converter 23 and the optical element 28is desirably about 0.2 μm. When the distance between the wavelengthconverter 23 and the optical element 28 is 0.3 μm, a little less thanhalf the heat generated by the wavelength converter 23 can be dissipatedfrom the optical element 28. When the distance between the wavelengthconverter 23 and the optical element 28 is 1 μm, 16% of the amount ofheat generated by the wavelength converter 23 is dissipated, and whenthe distance between the wavelength converter 23 and the optical element28 is 2 μm, 8% of the amount of heat generated by the wavelengthconverter 23 is dissipated. The blue light BL corresponding to 8% and16% of the generated heat is allowed to enter the optical element 28,whereby the amount of light emitted from the wavelength converter 23 canbe increased.

Effects of First Embodiment

The illuminator 2 according to the present embodiment includes the lightsource apparatus 20, which outputs the blue light BL, which belongs tothe first wavelength band, the wavelength converter 23, which convertsthe blue light BL into the fluorescence YL, which belongs to the secondwavelength band different from the first wavelength band, and theoptical element 28, which transmits the fluorescence YL emitted from thewavelength converter 23. The air layer 41 is provided between thewavelength converter 23 and the optical element 28, and has the lengthG1 along the direction of the optical axis ax3 of the optical element 28and greater than or equal to 0.3 μm but smaller than or equal to 9.0 μm.The optical element 28 has a coefficient of linear expansion smallerthan or equal to 65×10⁻⁷/° C. at temperatures ranging from 100° C. to200° C., and a thermal conductivity greater than or equal to 1.0 W/m·K.

According to the configuration described above, since the length G1 ofthe air layer 41 along the direction of the optical axis ax3 of theoptical element 28 is greater than or equal to 0.3 μm but smaller thanor equal to 9.0 μm, the amount of fluorescence YL leaking sideways fromthe gap between the wavelength converter 23 and the optical element 28can be reduced, and the divergence of the fluorescence YL due to themultiple-time reflection between the wavelength converter 23 and theoptical element 28 can be suppressed to a small amount. Since thefluorescence YL traveling from the wavelength converter 23 to theoptical element 28 recognizes the air layer 41, the fluorescence YL isrefracted by the air layer 41, and exits out of the optical element 28with the luminous flux diameter of the fluorescence YL reduced. Theilluminator 2 achieved by the present embodiment can therefore outputlight used by a downstream optical system at high light utilizationefficiency. Furthermore, since the coefficient of linear expansion ofthe optical element 28 is smaller than or equal to 65×10⁻⁷/° C. attemperatures ranging from 100° C. to 200° C., and the thermalconductivity of the optical element 28 is greater than or equal to 1.0W/m·K, there is little risk of damage to the optical element 28, and theheat from the wavelength converter 23 can be transferred and dissipatedout of the illuminator 2. Therefore, a rise in the temperature of thewavelength converter 23 can be suppressed, whereby a decrease in thewavelength conversion efficiency can be suppressed.

The illuminator 2 according to the present embodiment further includesthe spacer 33, which maintains the distance between the wavelengthconverter 23 and the optical element 28.

According to the configuration described above, using an appropriatelysized spacer 33 allows reliable control of the distance between thewavelength converter 23 and the optical element 28, that is, the lengthG1 of the air layer 41 between the wavelength converter 23 and theoptical element 28.

The illuminator 2 according to the present embodiment further includesthe first heat dissipating member 29, which is thermally coupled to theoptical element 28.

According to the configuration described above, the heat transferredfrom the wavelength converter 23 to the optical element 28 can befurther transferred to the first heat dissipating member 29. Thedissipation of the heat from the wavelength converter 23 can thus befurther facilitated, whereby the wavelength conversion efficiency can besufficiently maintained.

In the illuminator 2 according to the present embodiment, the opticalelement 28 includes the planar plate part 37 and the lens part 38.

According to the configuration described above, the planar plate part 37contributes to the heat dissipation from the wavelength converter 23,and the lens part 38 can contribute as a pickup lens that guides thelight from the wavelength converter 23 to a downstream optical system.

The illuminator 2 according to the present embodiment further includesthe reflection mirror 30, which is provided at a portion of the lenspart 38 and reflects the fluorescence YL emitted from the wavelengthconverter 23 toward the wavelength converter 23.

According to the configuration described above, the fluorescence YLexits through the opening 30 h of the reflection mirror 30, so that theluminous flux diameter of the fluorescence YL having exited out of theoptical element 28 is reduced, whereby the etendue can be reduced. Thefluorescence YL reflected off the reflection mirror 30 returns to thewavelength converter 23, is scattered by the pores 39, and is thenemitted again from the wavelength converter 23. Since the fluorescenceYL reflected off the reflection mirror 30 is thus recycled, theilluminator 2 achieved by the present embodiment can output light thatallows high light utilization efficiency.

The projector 1 according to the present embodiment, which includes theilluminator 2 according to the present embodiment, excels in the lightutilization efficiency.

Second Embodiment

A second embodiment of the present disclosure will be described belowwith reference to FIG. 8 .

The basic configurations of the projector and the illuminator accordingto the second embodiment are the same as those in the first embodiment,but differ therefrom in terms of how to ensure the distance between thewavelength converter and the optical element. The basic configurationsof the projector and the illuminator will therefore not be described.

FIG. 8 is a schematic configuration diagram of a wavelength conversionapparatus 52 according to the second embodiment.

In FIG. 8 , components common to those in the figures used in the firstembodiment have the same reference characters and will not be described.

The wavelength conversion apparatus 52 in the present embodimentincludes a wavelength converter 53, the optical element 28, the firstheat dissipating member 29, the reflection mirror 30, and the secondheat dissipating member 32, as shown in FIG. 8 . Unlike the wavelengthconversion apparatus 22 in the first embodiment, the wavelengthconversion apparatus 52 in the present embodiment does not include thespacer 33.

In the present embodiment, out of the two surfaces of the wavelengthconverter 53, a first surface 53 a and a second surface 53 b, the firstsurface 53 a facing the optical element 28 has irregularities 55.Protrusions and recesses that form the irregularities 55 have randomheights arranged in random intervals. The surface roughness Ra of thefirst surface 53 a is greater than or equal to 0.05 μm but smaller thanor equal to 0.2 μm. The surface roughness Ra is the average of theheights of the plurality of protrusions and the depths of the pluralityof recesses, and the maximum height of the plurality of protrusions andthe maximum depth of the plurality of recesses are typically about fivetimes the surface roughness Ra.

The distance between the wavelength converter 53 and the optical element28, that is, the length G1 of the air layer 41 along the direction ofthe optical axis ax3 of the optical element 28 is determined by theprotrusion having the maximum height out of the irregularities 55 of thefirst surface 53 a of the wavelength converter 53. Therefore, adjustingthe surface roughness Ra of the first surface 53 a to a value greaterthan or equal to 0.05 μm but smaller than or equal to 0.2 μm allows thelength G1 of the air layer 41 along the direction of the optical axisax3 of the optical element 28 to be a value ranging from 0.3 μm to 1.0μm, which corresponds to 5 times the surface roughness Ra of the firstsurface 53 a. The other configurations of the illuminator are the sameas those in the first embodiment.

Effects of Second Embodiment

The present embodiment also provides the same effects as those providedby the first embodiment, for example, the illuminator 2 achieved by thepresent embodiment can suppresses damage to the optical element 28 dueto heat, have high wavelength conversion efficiency, and output lightthat allows high light utilization efficiency.

In the illuminator 2 according to the present embodiment, the firstsurface 53 a, of the wavelength converter 53, which faces the opticalelement 28 has the irregularities 55. The surface roughness Ra of thefirst surface 53 a is greater than or equal to 0.05 μm but smaller thanor equal to 0.2 μm.

According to the configuration described above, the distance between thewavelength converter 53 and the optical element 28 can be controlled toa desired value without use of a spacer.

The technical scope of the present disclosure is not limited to theembodiments described above, and a variety of changes can be madethereto to the extent that the changes do not depart from the intent ofthe present disclosure. An aspect of the present disclosure can be anappropriate combination of the characteristic portions in theembodiments described above. For example, an illuminator according to anaspect of the present disclosure may include the spacer in the firstembodiment and the irregularities of the wavelength converter in thesecond embodiment.

For example, in the illuminator according to the embodiments describedabove, the planar plate part and the lens part of the optical elementare integrated with each other into a single unit, and the planar platepart and the lens part may instead be separate parts. For example, whenthe planar plate part is made of a glass or ceramic material, the planarplate part has a refractive index greater than or equal to 1.4. In thiscase, the fluorescence from the air layer enters the optical element atan angle of incidence smaller than or equal to 45°. That is, the planarplate part and the lens part can be formed of separate members, and theplanar plate part can be made of a material having high thermalconductivity. For example, the planar plate part has a thickness of 2 mmand is made of sapphire, quartz, calcium fluoride, or any other suitablematerial, and the lens part is made of high-refractive-index,low-dispersion glass. The planar plate part and the lens part may bejoined with each other or separate from each other with a distancetherebetween. The primary path along which the heat is conducted is thusmade of sapphire, quartz, calcium fluoride, or any other suitablematerial, allowing an increase in freedom in the choice of the materialof the lens part. Furthermore, coupling the periphery of the planarplate part to a heat dissipating member made, for example, of copperallows an increase in the cooling performance. On the other hand, thelens part made of high-refractive-index, low-dispersion glass allowsreduction in aberrations. When the planar plate part and the lens partface each other via curved surfaces, the fluorescence can be refractedby a greater amount, whereby the aberrations produced by the lens partcan be reduced. When the planar plate part and the lens part areseparate from each other with a distance therebetween, no heat istransferred to the lens part, so that heat-induced optical distortion isless likely to occur in the lens part.

The lens part may be configured to be moved in the form of eccentricrotation by using a hollow motor or any other drive source. The bluelight can therefore be moved repeatedly in the diameter direction, thediagonal direction, the direction of one side, or any other direction inthe region, of the wavelength converter, that is irradiated with theblue light. According to the configuration described above, thewavelength converter is scanned with the blue light, so that the heatgenerating area of the wavelength converter widens. The heat is thusdispersed, whereby the temperature of the wavelength converter can belowered.

To alternatively maintain the distance between the wavelength converterand the optical element, phosphor particles with the particle diametervariation suppressed to about ±30% with respect to a primary particlediameter ranging from 30 μm to 150 μm may be arranged on an aluminumsubstrate in the wavelength converter, and caused to firmly adhere tothe aluminum substrate with silicone or glass, and the optical elementmay be placed so as to be in contact with the upper surface of theresultant structure. In this case, in which the phosphor particlesconstitute the irregularities, when the fluorescence is reflected offthe first surface of the optical element and then impinges on thephosphor particles, the traveling direction of the fluorescence changesat the surfaces of the phosphor particles. The same effects as thoseprovided by the embodiments described above can thus be provided.

In addition to the above, the specific descriptions of the shapes, thenumbers, the arrangements, the materials, and other factors of thecomponents of the illuminator and the projector are not limited to thosein the embodiments described above and can be changed as appropriate.The above embodiments have been described with reference to the casewhere the illuminator according to the present disclosure isincorporated in a projector using liquid crystal panels, but notnecessarily. The illuminator according to the present disclosure may beused in a projector using a digital micromirror device as each of thelight modulators. The projector may not include a plurality of lightmodulators and may instead include only one light modulator.

The aforementioned embodiments have been described with reference to thecase where the illuminator according to the present disclosure isincorporated in a projector, but not necessarily. The illuminatoraccording to the present disclosure may be used as a lighting apparatus,a headlight of an automobile, and other components.

An illuminator according to an aspect of the present disclosure may havethe configuration below.

The illuminator according to the aspect of the present disclosureincludes a light source that outputs first light that belongs to a firstwavelength band, a wavelength converter that converts the first lightinto second light that belongs to a second wavelength band differentfrom the first wavelength band, and an optical element that transmitsthe second light emitted from the wavelength converter. An air layer isprovided between the wavelength converter and the optical element, andhas a length along the direction of the optical axis of the opticalelement and greater than or equal to 0.3 μm but smaller than or equal to9.0 μm. The optical element has a coefficient of linear expansionsmaller than or equal to 65×10⁻⁷/° C. at temperatures ranging from 100°C. to 200° C., and a thermal conductivity greater than or equal to 1.0W/m·K.

The illuminator according to the aspect of the present disclosure mayfurther include a spacer that maintains the distance between thewavelength converter and the optical element.

In the illuminator according to the aspect of the present disclosure,the surface, of the wavelength converter, that faces the optical elementmay have irregularities.

In the illuminator according to the aspect of the present disclosure,the surface roughness of the surface may be greater than 0.05 μm butsmaller than or equal to 0.2 μm.

The illuminator according to the aspect of the present disclosure mayfurther include a heat dissipating member thermally coupled to theoptical element.

In the illuminator according to the aspect of the present disclosure,the optical element may include a planar plate part and a lens part.

In the illuminator according to the aspect of the present disclosure,the planar plate part and the lens part may be separate parts.

The illuminator according to the aspect of the present embodiment mayfurther include a reflection mirror that is provided at a portion of thelens part and reflects the second light emitted from the wavelengthconverter toward the wavelength converter.

A projector according to another aspect of the present disclosure mayhave the configuration below.

The projector according to the other aspect of the present disclosureincludes the illuminator according to the aspect of the presentdisclosure, a light modulator that modulates light outputted from theilluminator and containing the second light in accordance with imageinformation, and a projection optical apparatus that projects the lightmodulated by the light modulator.

What is claimed is:
 1. An illuminator comprising: a light source thatemits first light that belongs to a first wavelength band; a wavelengthconverter that converts the first light into second light that belongsto a second wavelength band different from the first wavelength band;and an optical element that transmits the second light emitted from thewavelength converter, wherein an air layer is provided between thewavelength converter and the optical element, a length of the air layeralong a direction of an optical axis of the optical element is greaterthan or equal to 0.3 μm but smaller than or equal to 9.0 μm, and theoptical element has a coefficient of linear expansion smaller than orequal to 65×10⁻⁷/° C. at temperatures ranging from 100° C. to 200° C.,and a thermal conductivity greater than or equal to 1.0 W/m·K.
 2. Theilluminator according to claim 1, further comprising a spacer thatmaintains a distance between the wavelength converter and the opticalelement.
 3. The illuminator according to claim 1, wherein a surface, ofthe wavelength converter, that faces the optical element hasirregularities.
 4. The illuminator according to claim 3, wherein surfaceroughness of the surface is greater than or equal to 0.05 μm but smallerthan or equal to 0.2 μm.
 5. The illuminator according to claim 1,further comprising a heat dissipating member thermally coupled to theoptical element.
 6. The illuminator according to claim 1, wherein theoptical element includes a planar plate part and a lens part.
 7. Theilluminator according to claim 6, wherein the planar plate part and thelens part are separate parts from each other.
 8. The illuminatoraccording to claim 6, further comprising a reflection mirror provided ata portion of the lens part, the reflection mirror configured to reflectthe second light emitted from the wavelength converter toward thewavelength converter.
 9. A projector comprising: the illuminatoraccording to claim 1; a light modulator that modulates light emittedfrom the illuminator and containing the second light; and a projectionoptical apparatus that projects the light modulated by the lightmodulator.